Transmitting apparatus, sound sensor and autonomous traveling vehicle

Abstract

A driving circuit of a transmitting apparatus drives a piezoelectric element in a frequency band different from a resonance frequency at which a vibration system including the piezoelectric element resonates the most strongly. A driving circuit of a sound sensor drives the piezoelectric element for transmitting or receiving an acoustic wave in a frequency band different from a resonance frequency at which a vibration system including the piezoelectric element resonates the most strongly. Such a transmitting apparatus is mounted as a transmitting apparatus of a sound sensor to thereby realize the sound sensor with a small measurement error. The sound sensor is adopted for traveling control and steering control of an autonomous traveling vehicle to thereby enable an autonomous traveling vehicle capable of stopping in the vicinity of an obstacle to be realized.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2004-104391 filed in Japan on Mar. 31, 2004, the entire contents of which are hereby incorporated by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The invention relates to a transmitting apparatus and a sound sensor for obtaining information such as the presence / absence of a detection-target object with an acoustic wave, or a distance therefrom to the detection-target object, and further relates to an autonomous traveling vehicle equipped with such a sound sensor. [0004] 2. Description of Related Art [0005] Conventionally, there has been known an ultrasonic sensor that transmits an ultrasonic wave to a detection-target object and, also, receives a reflected wave from the detection-target object to thereby measure a distance therefrom to the detection-target object on the basis of an elapsed time from a trans...

AI Technical Summary

Benefits of technology

[0012] The present inventors conducted researches including experiments with serious efforts for the purpose of decreasing a measurement error revealed as a time T2 shown in FIG. 1C mentioned above. Through the research, the present inventors have found that a response time of a vibration system including a piezoelectric element is reduced in a case where a frequency which drives the piezoelectric element is set to a frequency different from a frequency at which the vibration system including the piezoelectric element resonates the most strongly, which is dissimilar to that in a conventional way, to thereby cause a steep rise of acoustic pressure of an ultrasonic wave transmitted by the vibration system, with the result that the time T2 shown in FIG. 1C can be greatly reduced, that is, the measurement error can be considerably reduced.

[0014] The invention also aims to provide a sound sensor having a small measurement error by adopting a configuration in which a piezoelectric element is driven in a frequency band different from a resonance frequency at which a vibration system including the piezoelectric element commonly used in transmission / reception of an acoustic wave resonates the most strongly.

[0017] In the transmitting apparatus according to the first aspect of the invention, the driving circuit applies to the piezoelectric element a voltage that alters in a frequency band different from a resonance frequency at which a vibration system including the piezoelectric element resonates the most strongly. Since the piezoelectric element vibrates by applying a voltage from the driving circuit, an acoustic wave is transmitted. By driving the piezoelectric element in a frequency band different from a resonance frequency at which the vibration system including the piezoelectric element resonates the most strongly, a response time of the vibration system becomes shorter and a rise of acoustic pressure of an acoustic wave becomes steep as compared with a case where the piezoelectric element is driven in frequency at which the vibration system including the piezoelectric element resonates the most strongly.

[0024] According to the transmitting apparatus of the first aspect of the invention, a response time becomes shorter, a rise of acoustic pressure of an acoustic wave becomes steep, so that a measurement error generated in an input waveform of the receiver becomes smaller as compared with a case where the piezoelectric element is driven in a resonance frequency at which the vibration system including the piezoelectric element resonates the most strongly.

[0025] According to the sound sensor of the second aspect of the invention, since an elapsed time until an acoustic pressure of an acoustic wave received by the receiving apparatus takes a predetermined value from the time when the acoustic wave reaches the receiving apparatus becomes shorter, an elapsed time until the acoustic wave actually exceeds a threshold value for use in determination of having detected from the time when the acoustic wave actually reaches the receiving apparatus becomes shorter, which makes a measurement error smaller.

[0026] According to the autonomous traveling vehicle of the third aspect of the invention, since a measurement error of the sound sensor becomes smaller to thereby enable a distance therefrom to the detection-target object with a high accuracy, an event in which the vehicle collides with the detection-target object because of a delay in control for stoppage is prevented from occurring.

Problems solved by technology

The conventional sound sensor has had an unsolved problem that a measurement error, to be concrete, the time T2 shown in FIG. 1C, indispensably arises due to such a slow rise of acoustic pressure of an ultrasonic wave.

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